1. Field of the Invention
The present invention relates to an adjustable reflector of a head-up display, and more particularly, to an adjustable reflector of a head-up display capable of improving image stability.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is a diagram showing a head-up display of the prior art. Generally, the head-up display 100 of the prior art comprises an image source 110, a lens 120, a reflecting mirror 130 and an optical combiner 140. A light beam L generated by the image source 110 is refracted by lens 120, and then reflected to the optical combiner 140 by the reflecting mirror 130. The light beam L reflected to the optical combiner 140 forms a virtual image and/or a real image for providing driving information, such as vehicle speed information, time information and navigation information, to a driver. Since different drivers have different heights and seating positions, in order to allow the drivers to easily see the information displayed by the head-up display, a reflection angle of the reflecting mirror 130 can be adjusted to reflect the light beam L to an appropriate position on the optical combiner 140. For example, when the driver is shorter, the head-up display 100 can rotate the reflecting mirror 130 for moving an incident position of the light beam L from a first position P1 to a second position P2, which is a lower position, on the optical combiner 140. However, an imaging distance of the virtual image and/or the real image on the optical combiner 140 is related to a travelling distance of the light beam L from the lens 120 to the optical combiner 140, and a focal length of the lens 120 is fixed. When the incident position of the light beam L is moved from the first position P1 to the second position P2 on the optical combiner 140, the travelling distance of the light beam L from the reflecting mirror 130 to the optical combiner 140 becomes shorter (changed from a2 to a3), such that the imaging distance of the virtual image and/or the real image is changed, so as to affect image quality of the virtual image and/or the real image. Moreover, when the incident position of the light beam L is moved from the first position P1 to the second position P2 on the optical combiner 140, an incident angle of the light beam L is also changed, so as to further cause image distortion. Therefore, when the head-up display 100 of the prior art adjusts the reflection angle of the reflecting mirror 130, the head-up display 100 has lower image stability.